Which are the minerals found in soil?« Back to Questions List

Soil contains a large number of minerals which can be broadly classified into two categories namely, primary and secondary. These minerals can be separated after removing extraneous substances from soil. By scientific definition, a mineral is an inorganic substance produced by natural process and contains definite composition. 

The original composition of rock is called primary mineral. Secondary minerals are formed when primary mineral undergoes various changes. Secondary minerals are complex in nature with specific physio-chemical properties. The properties of a rock are often defined by the nature of minerals contained therein. The minerals present in rocks are called essential minerals and the main among them are quartz, pyroxenes, feldspars, mica, olivine, amphiboles etc. 

The primary minerals are also known as skeletal minerals.  Primary minerals when present in soil differ greatly in their oxide content. The optical properties of silicates are very important for their identification. They are normally identified through petrographic microscope and measured by assessing refractive indices. But, opaque minerals are identified on the basis of the appearances  of their surfaces in reflected light. 

The most abundant mineral in rocks and soil is quartz. It is also present in clay. Feldspars are a series of silicates of aluminum with potassium, calcium or sodium as a major component. The pyroxene and amphibole groups include of minerals that vary in mineralogical and chemical properties. The pyroxenes are normally less complex than the amphiboles. 

Clay soil is constituted by secondary minerals. The clay minerals are mostly crystalline in shape. Small fractions of organic matter are also present in clay. Techniques like electron diffraction analysis and X-ray diffraction analysis are performed to identify specific properties of clay minerals. A beam of electrons with high energy content behaving like a wave is employed to understand the crystal structure in electron diffraction analysis. The energy loss is assessed to study the crystal structure.  In X-ray diffraction method, X-rays are employed and from the pattern of diffraction, the crystal structure is arrived. X-ray diffraction analysis often takes more time compared to electron diffraction technique. 
 

How is water retained by the soil?

Minerals: Sources And Roles In The Functioning of Body